Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Gamping - Airbnb for camping - Camping with a local
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Hipcamp - Book unique camping experiences on over 300,000 campsites, cabins, RV parks, public parks and more.
Bigtent - BigTent is a web-based organization and communication portal for groups.
Wildpoint - The Airbnb of camping